The employment of magnetoresistive (MR) sensors for reading signals from media is well known. Such sensors read signals from the media by detecting a change in resistance of the sensor due to magnetic fields from the media. Many variations of MR sensors are known, such as anisotropic magnetoresistive (AMR) sensors, dual stripe magnetoresistive (DSMR) sensors, giant magnetoresistive (GMR) sensors, spin valve (SV) sensors and dual spin valve (DSV) sensors.
Common to these sensors is the need to provide bias fields, both to eliminate noise and to facilitate signal readout. A known means for biasing the sensor involves abutting a permanent magnet to ends of the sensor, the magnet preferably forming a contiguous junction across plural sensor layers. Conductive leads, which may be separate from the biasing means, may also adjoin sensor layers along a contiguous junction.
In order to form a contiguous junction, a sensor is usually deposited in layers and then its border defined by masking and ion beam milling or etching (IBE), reactive ion etching (RIE) or the like. Ideally, milling could be performed that directs an ion beam exactly perpendicular to the surface on which the MR sensors are being formed, resulting in blunt sensor ends that terminate at a 90.degree. angle to that surface. Redeposition of materials removed by milling and other complications interfere with this scenario, however, so that such exact etching is not practicable. Moreover, following such a perpendicular IBE the deposition of hard bias and/or conductor layers could blanket the mask, so that etching of the mask would be prevented and the necessary lift-off of these layers would become problematic.
A known means for forming a contiguous junction involves forming an undercut in the mask and rotating the IBE at an angle offset from 90.degree.. FIG. 1 exemplifies this approach, in which a magnetic shield 20, insulative layer 22 and sensor 25 has been formed atop a substrate 27. A bi-layer resist 28 and 29 has been photolithographically patterned atop the layers that are to form the sensor 25, leaving an undercut 30 closest to the sensor. An IBE is directed at a relatively rotating angle to perpendicular to form a curved border 33 for which part of the insulative layer as well as all of the sensor layers have been removed. Dotted lines 35 and 37 represent directions of the rotating ion beam at opposite phases, and show that etching proceeds less beneath the mask where line 37 impinges but not line 35. The removal of part of layer 22 is termed overmilling. The undercut 30 allows etchant to remove the mask 28 even after deposition of hard bias and lead layers that cover the mask as well as adjoin the border 33 to form a contiguous junction.
The shallow slope of the resulting contiguous junction has a number of drawbacks. The oblique angle of the border defining the contiguous junction denigrates the bias field provided to the sensor and complicates the sensor domain structures, so that noise is not eliminated. The shallow slope also creates inaccuracy in the width of the sensor, which ideally should match the width of magnetic tracks on the media, called the "track width." Surprisingly, the length of the contiguous junction regions on both ends of the sensor can be comparable to or even greater than the width of the sensor between the contiguous junction regions, blurring images and causing off-track errors.
The contiguous junction 33 could be made more blunt along the sensor with additional ion milling into the insulative layer 22, also known as the read gap. Unfortunately this may result in electrical shorting between the shield and the hard bias and lead layers. The insulative layer 22 can be made thicker to allow for this overmilling, but the thickness of that read gap separating the sensor from the shield is a primary determinant of the resolution of the sensor. In other words, the sensor "sees" magnetic fields from the media that pass between the shields, and the closer the shields are to the sensor the more narrow the focus of the sensor. Thus an attempt to create a less oblique contiguous junction to solve the bias and resolution problems can result in other resolution problems and electrical shorting.